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 ###Instrução: Qual é a noção quando a estrutura cristalina é tetragonal e a fórmula é bi 2 sr 2 cacu 2 o 8.
 ###Tabelas: CREATE TABLE ethnic_groups_and_demographics (ethnic_groups_and_demographics_id AUTO_INCREMENT PRIMARY KEY, Raion (district) or City VARCHAR, Total VARCHAR, Ukrainians VARCHAR, Moldovans VARCHAR, Bessarabian Bulgarians VARCHAR, Russians VARCHAR, Gagauzians VARCHAR, Other ethnic groups² VARCHAR) CREATE TABLE bi-_tl-_and_hg-based_high-__c__superconductors (bi-_tl-_and_hg-based_high-__c__superconductors_id AUTO_INCREMENT PRIMARY KEY, Formula VARCHAR, Notation VARCHAR, T c (K) INT, No. of Cu-O planes in unit cell INT, Crystal structure VARCHAR) CREATE TABLE wins_50 (wins_50_id AUTO_INCREMENT PRIMARY KEY, Outcome VARCHAR, Date VARCHAR, Tournament VARCHAR, Surface VARCHAR, Partner VARCHAR, Opponents in the final VARCHAR, Score in the final VARCHAR) CREATE TABLE passenger_and_express_train_locomotives (passenger_and_express_train_locomotives_id AUTO_INCREMENT PRIMARY KEY, Class VARCHAR, Railway number(s) VARCHAR, Quantity INT, Year(s) of manufacture VARCHAR, Axle arrangement VARCHAR) CREATE TABLE participating_schools (participating_schools_id AUTO_INCREMENT PRIMARY KEY, School VARCHAR, Location VARCHAR, Enrolment INT, Founded INT, Denomination VARCHAR, Day/Boarding VARCHAR, School Colours VARCHAR, Abbreviation VARCHAR, In competition since INT)  
SELECT Notation FROM bi-_tl-_and_hg-based_high-__c__superconductors WHERE Crystal structure = Tetragonal AND Formula = Bi 2 Sr 2 CaCu 2 O 8